The present invention relates generally to an apparatus for low temperature refrigeration systems. More particularly, the present invention elates to a non-hydrochlorofluorocarbon (non-HCFC) design of a refrigerant mixture for an ultra-low temperature refrigeration system.
In refrigeration systems, a refrigerant gas is compressed in a compressor unit. Heat generated by the compression is then removed generally by passing the compressed gas through a water or air cooled condenser coil. The cooled, condensed gas is then allowed to rapidly expand into an evaporating coil where the gas becomes much colder, thus cooling the coil and the inside of the refrigeration system box around which the coil is placed.
Ultra-low and cryogenic temperatures ranging from xe2x88x9295xc2x0 C. to xe2x88x92150xc2x0 C. have been achieved in refrigeration systems using a single circuit vapor compressor. These systems typically use a single compressor to pump a mixture of four or five chlorofluorocarbon (CFC) containing refrigerants to reach an evaporative temperature of as low as xe2x88x92160xc2x0 C.
Environmental concern over the depletion of the ozonosphere has increased pressure on refrigerator manufacturers to substantially reduce the level of CFC-containing refrigerants used within their systems. Although non-CFC refrigerant mixtures have been developed, it has been discovered that most of these refrigerant mixtures cannot simply be substituted for CFC-containing refrigerants in currently available refrigeration systems due to the different thermodynamic properties of the refrigerants.
The present inventor has discovered that using non-CFC refrigerants in conventional ultra-low and cryogenic temperature systems cause an imbalanced flow of the refrigerants in the refrigeration circuit, which reduces the cooling capability of the refrigerants to the compressor. Such low levels of compressor cooling can cause a system to fail due to compressor overheating.
Furthermore, given that HCFC refrigerants do contain chlorine, that over time can affect the ozone layer as well as CFC refrigerants, the present inventor has developed a novel autocascade ultra-low and cryogenic temperature refrigeration system which is capable of operating with non-HCFC refrigerant mixtures. These non-HCFC refrigerant mixtures are non-toxic, chemically stable, commercially available and compatible with most of the standard refrigeration oils and compressor materials. Normally, one component of a non-CFC refrigerant mixture, i.e., hydrochlorofluorocarbon (HCFC), is a regulated ozone depleting chemical. However, the present invention uses a non-HCFC refrigerant mixture which has no ozone depleting properties at all, i.e., the mixture is primarily composed of hydrofluorocarbon (HFC) refrigerants and hydrocarbons.
As shown in FIG. 7, an index called the Ozone Depletion Potential (ODP) has been adopted for regulatory purposes. The ODP of a compound is an estimate of the total ozone depletion due to 1 Kg of the compound divided by the total ozone depletion due to 1 Kg of CFC-11 refrigerant. Thus, the ODP shows relative effects of comparable emissions of the various compounds.
Unlike the CFC-containing refrigeration systems which do not cause overheating of the compressor, the present inventor has discovered that the substantially non-HCFC refrigeration systems must provide additional liquid return to the compressor in order to avoid overheating thereof and eventual failure of the system.
The present inventor has been able to overcome the overheating of the compressor when using substantially non-HCFC refrigerants in a single compressor autocascade system. This is accomplished by providing a specially-designed capillary tube or expansion means disposed downstream of the first liquid/gas separator such that liquid refrigerants are returned directly to the auxiliary condenser and then to the compressor. This feature enables larger than normal quantities of refrigerants of higher boiling points to be rapidly returned to the compressor, which results in excellent operating conditions of the compressor and avoids overheating thereof.
As such, the overall performance of the non-HCFC autocascade system is comparable to its counterpart of the CFC autocascade system. This is evidenced by the fact that both systems have similar pull down rates and compressor operating conditions at standard 90xc2x0 F. ambient.
The present invention also provides many additional advantages which shall become apparent as described below.
The present invention overcomes the need for using CFC or HCFC refrigerant mixtures in a refrigeration system by utilizing refrigerants R14, R23, R50, R116, R134a, R152a, R170, R236fa, R236ea, R245fa, R245ca, RC318, R290, RR508a, R508b, R600, R600a, R740 and R 1150 in various 5, 6 and 7-component mixtures. To achieve desired properties, these refrigerants may be used in a xe2x80x9ccocktailxe2x80x9d mixture (e.g., R600a or R600; R290; R170 or R 1150; R50; and R740).
It is therefore a feature of the present invention to provide a non-HCFC ultra-low temperature refrigerant mixture that can safely be applied in the field as needed without the risks associated with CFC or HCFC ultra-low temperature refrigerants.
It is another feature of the present invention to provide a refrigeration heat exchanger section which is capable of circulating a substantially non-HCFC refrigerant mixture which comprises: a compressor means, an auxiliary condenser, a first condenser, a second condenser, a third condenser, a subcooler means and a liquid/gas separator, wherein the improvement is characterized by: a means for distributing a subcooled refrigerant liquid mixture from the liquid/gas separator to a first expansion means and a second expansion means for forming first and second expanded streams, respectively; and a first conduit means for returning the first expanded stream to the auxiliary condenser and the compressor; and a second conduit means for delivering the second expanded stream to the first condenser.
More specifically, the refrigeration heat exchanger section preferably comprises: a compressor means; an auxiliary condenser connected to receive and cool the refrigerant mixture discharged from the compressor means; a first liquid/gas separator connected to received the cooled refrigerant mixture discharged from the auxiliary condenser, wherein a subcooled refrigerant liquid mixture is taken as bottoms and a gaseous refrigerant liquid mixture is taken overhead; a means for distributing the subcooled refrigerant liquid mixture to a first expansion means and a second expansion means to form a first expanded stream and a second expanded stream, respectively; a first conduit means for returning the first expanded stream to the auxiliary condenser and the compressor.
The high pressure flow of the heat exchanger circuit further comprises: a first condenser connected to receive the gaseous refrigerant mixture from the liquid/gas separator; a second liquid/gas separator connected to receive the gaseous refrigerant mixture from the first condenser, wherein a subcooled liquid refrigerant mixture is taken as bottoms and a gaseous refrigerant mixture is taken overhead; a second condenser connected to receive the gaseous refrigerant mixture which is taken overhead from the second liquid/gas separator; a third condenser connected to receive at least a portion of the gaseous refrigerant mixture taken from the second condenser; and a subcooler means connected to receive the gaseous refrigerant mixture from the third condenser.
The low pressure flow of the heat exchanger circuit further comprises: a distributor means connected to receive the refrigerant mixture from the subcooler means, the distributor means is capable of separating the refrigerant mixture into a first stream and a second stream; a third expansion means connected to receive the first stream, thereby forming a third expanded stream; a third conduit means for delivering the third expanded stream to the subcooler means; a fourth expansion means connected to received the second stream, thereby forming a fourth expanded stream; a fourth conduit means for delivering the fourth expanded stream to a storage tank; a fifth conduit means for delivering the fourth expanded stream from the storage tank to the third condenser; a sixth conduit means disposed between the third condenser and the second condenser such that the fourth expanded stream from the third condenser is delivered to the second conduit means; a sixth expansion means connected to receive the subcooled liquid refrigerant mixture from the second liquid/gas separator, thereby forming a fifth expanded stream; a seventh conduit means for delivering the fifth expanded stream to the second condenser; an eighth conduit means for delivering the fifth expanded stream from the second condenser to the first condenser; a second conduit means for delivering the second expanded stream to the first condenser; a ninth conduit means for delivering the second expanded stream and the fifth expanded stream from the first condenser to the auxiliary condenser; and a tenth conduit means for delivering the first, second and fifth expanded streams from the auxiliary condenser to the compressor.
There has been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of he invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purposes of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent construction insofar as they do not depart from the spirit and scope of the present invention.